1. Field of the Invention
This invention relates to an impact printer and more particularly to a wire matrix printer having a stored energy printhead.
2. Description of the Prior Art
In matrix printing, the wire matrix employed in forming each alpha-numeric character is defined by a predetermined number of impressions arranged in a column which may be vertical or inclined and which is advanced to a predetermined number of laterally spaced positions, or submultiples thereof. For example, a 9.times.9 matrix is comprised of nine print members, each capable of printing a dot in the column in each of nine parallel columns. By controlled vertical and horizontal additional printing of dots, through various known techniques, a higher quality font may be obtained.
In the past, a plunger magnet type wire matrix printhead has been employed. Each print member is driven by its own solenoid with the activation ends thereby being spread rather widely apart and with the impression ends being very close together. This requires the use of a long, curved wire which involves various problems such as breakage and wear. This type of head is shown in U.S. Pat No. 4,091,909.
Another prior art head is the clapper type which involves an armature that strikes the print member (ballistic type) or is attached to the print member (solid type). The solid type is more suitable for high-speed operation than the ballistic type because it involves no collision between the armature and the print member.
More recently, a stored energy or spring charge type wire matrix printhead has been employed for particularly high-speed applications. In this type, a leaf spring connected to each print member is flexed by a magnetic field. By selectively overcoming that field, the flexed leaf spring drives the print member into contact with the paper. The disadvantage of this high-speed printhead is the large amount of power required and the resultant heat generated in the head.
The present invention has the advantages of the stored energy printhead, but has a drastic reduction in the power required and therefor in operational temperature.